Hydrocarbons may be removed from a subterranean formation by drilling a wellbore traversing the subterranean formation. The wellbore may be complex and may include, for example, multilateral wellbores and sidetrack wellbores. A multilateral wellbore includes one or more secondary wellbores that extend from a parent (or main) wellbore, while a sidetrack wellbore can include a main wellbore in a first direction and a secondary wellbore diverted from the main wellbore in a second general direction. Accordingly, a casing string assembly within one of these complex wellbores may include a window or opening in the wall of a casing to allow intersecting wellbores, such as a lateral wellbore or a sidetrack wellbore, to be formed. The window may be pre-milled or otherwise created before the casing string assembly is positioned in the wellbore. Casing with pre-milled windows are used to reduce or eliminate debris during the drilling process. The pre-milled window must be protected prior to drilling.
The figures referred to above are not drawn necessarily to scale and should be understood to present a representation of an embodiment and to illustrate the principles involved. Some features of the casings depicted in the drawings have been enlarged or distorted relative to others to facilitate explanation and understanding. The same reference numbers are used in the drawings for similar or identical components and features shown in various alternative embodiments. Casings, as disclosed herein, will have configurations and components determined, in part, by the intended application and environment in which they are used.